President Reagan thinks that people should migrate, like birds. They can, he has often said, "vote with their feet." At his latest press conference, when asked about people who might find themselves in uncongenial states, he indicated they should just move along.

He was asked twice about people who cannot afford to move. He did not answer.

It seems there are people who, like certain birds, do not choose to go to softer climes. No one asks the birds why they don't take wing, why they shiver on windowsills waiting for the unreliable handouts. They simply choose to stay. People choose to stay in Minneapolis, where the temperature goes to 40 below. They live in Gary, Ind. Some people have a thing for Toledo.

Some even choose to live in Middletown, Pa., under the shadow of two nuclear towers, one of which was the site of the worst accident in the history of commercial nuclear power. Three from Middletown came to Washington this week to carry on their fight with the Nuclear Regulatory Commission, which proposes to reopen TMI-1, the undamaged Three Mile Island nuclear reactor. They are members of PANE--People Against Nuclear Energy.

Linda Lotz, Paola Kinney and Joyce Corradi are not your usual nuclear protesters. They are not peripatetic intellectuals out to save the world from the mushroom cloud. They are working-class women, who want to save their children. Instead of wine and cheese receptions for the cause, they run bake sales.

None of them was politically involved, none ever doubted the words of General Public Utilities or Metro Edison about the safety, cleanliness and efficiency of nuclear power--never, that is, until March 28, 1979, when the sirens sounded and they didn't know where their children were.

That day changed their lives. They have been badgering the utility executives and banging on the doors of the Nuclear Regulatory Commission ever since.

Even if they wanted to follow Reagan's advice to clear out, they can't. They can't sell their houses, for one thing. Real estate values are, understandably, depressed in Middletown. But beyond that, they want to stay because, however hazardous, Middletown is home. The NRC refused them a hearing about the psychological stress and community fears that they claim as reasons for not restarting TMI-1. But they hired a lawyer and went to court. And they won.

A judgment by the Circuit Court of Appeals--it is not yet in opinion form--may make it possible for them to live in their town with easy minds. The court ruled that the NRC could not restart TMI-1 until it makes "an environmental assessment on the pscyhological health of neighboring residents and on the well-being of the surrounding communities."

The judgment could have a profound effect on the future of Three Mile Island and nuclear power in general, even if it doesn't apply to plants under construction in less populated areas. The president has resoundingly endorsed nuclear energy, but the utilities are finding out that making plants safe is an almost prohibitively expensive business.

In his dissent, Judge Malcolm Wilkey complained that psychological impact was "never before considered as covered by the National Environmental Policy Act."

But the stress, according to the Middletown women, is constant. They received with their township tax bill last year an evacuation plan, which threw them into further consternation. Under its provisions, parents being evacuated were forbidden to go and find their children.

Says Joyce Corradi, the mother of three, "If there is an evacuation, which one of my children would I go for first? They go to three different schools, one of them 25 miles away. Every time we hear a siren, we freeze. People say, 'Is it the Island?' The last time we were evacuated I forgot my marriage certificate and the family photos. I have them ready if there's another time."

The startup of TMI-1 is closely related to the cleanup of the damaged reactor, TMI-2, a halting enterprise watched with great trepidation by the community. The utility companies want the reopening for financial as well as symbolic reasons. Resumption of service would help somewhat to defray the staggering cleanup bill, which is estimated at $500 million.

Sen. Mark Hatfield (R-Ore.), chairman of the Senate Appropriations Commmittee, is holding hearings in Harrisburg on Gov. Richard Thornburgh's proposal that other states contribute to the cleanup fund. It has little support in Congress.

The Middletown women are fearful that friends of the ailing industry will introduce legislation to reverse the Appeals Court decision. The utilities are lobbying for such a bill. The NRC has ordered an environmental assessment.

If they're lucky, the women could help make the whole country safer.

In the meantime, they make it clear why people don't take up Reagan's airy challenge to "vote with their feet." Some Americans would rather fight than switch.